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Monitoring External and Internal Loads of Brazilian Soccer Referees

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Monitoring External and Internal Loads of Brazilian Soccer Referees
©Journal of Sports Science and Medicine (2013) 12, 559-564
http://www.jssm.org
Research article
Monitoring External and Internal Loads of Brazilian Soccer Referees during
Official Matches
Eduardo C. Costa 1, Caio M. A. Vieira 1, Alexandre Moreira 2, Carlos Ugrinowitsch 2, Carlo
Castagna 3 and Marcelo S. Aoki 4
1
Departament of Physical Education, Federal University of Rio Grande do Norte, Brazil; 2 School of Physical Education
and Sport, University of São Paulo, Brazil; 3 Football Training and Biomechanics Laboratory, Italian Football Federation (FIGC), Technical Department, Coverciano (Florence), Italy; 4 School of Arts, Sciences and Humanities, University
of São Paulo, Brazil.
Abstract
This study aimed to assess the external and internal loads of
Brazilian soccer referees during official matches. A total of 11
field referees (aged 36.2 ± 7.5 years) were monitored during 35
matches. The external (distance covered, mean and maximal
speed) and internal load parameters (session ratings of perceived
exertion [RPE] training load [TL], Edwards’ TL, and time spent
in different heart rate [HR] zones) were assessed in 3-4 matches
per referee. External load parameters were measured using a
wrist Global Positioning System (GPS) receiver. No differences
in distance covered (5.219 ± 205 vs. 5.230 ± 237 m) and maximal speed (19.3 ± 1.0 vs. 19.4 ± 1.4 km·h-1) were observed
between the halves of the matches (p > 0.05). However, the
mean speed was higher in the first half of the matches (6.6 ± 0.4
vs. 6.4 ± 0.3 km·h-1) (p < 0.05) than in the second half. The
mean HR during the matches was ~89% of HRmax. In ~95% of
the matches, the referees demonstrated a HR ≥ 80% of HRmax.
Nonetheless, the time spent at 90-100% of HRmax was higher in
the first half (59.9 vs. 52.3%) (p < 0.05). Significant correlations
between session RPE TL and distance covered at 90-100% of
HRmax (r = 0.62) and session RPE TL and maximal speed (r =
0.54) (p < 0.05) were noted. Furthermore, there was a positive
correlation between session RPE TL and Edwards’ TL (r = 0.61)
(p < 0.05). Brazilian soccer referees demonstrated high external
and internal load demands during official matches. The portable
GPS/HR monitors and session RPE method can provide relevant
information regarding the magnitude of the physiological strain
during official matches.
Key words: Match activity, heart rate, session ratings of perceived exertion, training load, GPS receiver.
Introduction
Soccer is characterized as an intermittent sport in which
energy production is heavily dependent upon aerobic
metabolism (Reilly, 1997; Impellizzeri et al., 2004; 2005;
Stølen et al., 2005). During an official match, elite-level
field players run between 10 and 12 km at an average
intensity that is close to the anaerobic threshold (80-90%
of maximal heart rate). Players also perform several explosive activities such as sprinting, jumping, tackling,
changes in direction, high-intensity running and sustained
forceful contractions to maintain balance and control of
the ball under the pressure of defensive players (Bangsbo
et al., 2008; Krustrup et al., 2006; Stølen et al., 2005).
The physical demand of elite soccer players also
affects the activity of the referees (Castagna et al., 2007;
Weston et al., 2012). Weston et al. (2007) were the first to
demonstrate a correlation between match activity of elite
soccer players and soccer referees. During a competitive
match, an elite soccer referee covers 9-13 km at 85-90%
of the maximal heart rate (HRmax) and 70-80% of the
maximal oxygen uptake (VO2max) (Castagna et al., 2007;
Weston et al., 2012). Like field players, referees cover a
significant amount of the total distance at high-intensity
(Castagna et al., 2007; Weston et al., 2011b; 2012). Thus,
the physical training of referees should employ TL capable of inducing specific physiological adaptations. In this
scenario, monitoring the external (e.g. distance covered,
mean speed, quantity of low, moderate and high-intensity
running) and internal loads (e.g., mean HR, time and
distance spent in zones of HR, blood lactate concentration) during official matches is crucial to improve the
accuracy of the training prescription and recovery.
When assessing the physical demands (external
loads) of soccer referees during official matches, previous
studies have used different parameters such as total distance covered, distance covered at different intensities
(i.e., low, medium, high, and sprinting), and distance
covered using different movement patterns (e.g., backward and sideward) per match, in different soccer leagues
(Castagna et al., 2007). Even though data regarding the
external load are abundant, less attention has been devoted to determining the internal load during official
matches, including markers as HR and ratings of perceived exertion (RPE) (Mallo et al., 2009; Weston et al.,
2006; 2010). The assessment of the internal load requires
the quantification of the physiological strain imposed on
the organism (Impellizzeri et al., 2005). Several methods
have been proposed attempting to quantify the physiological strain. The HR and session RPE methods (Foster
et al., 2001; Banister, 1991; Edwards, 1993; Lucia et al.,
2003) have been successfully used for determining the
internal load associated with soccer matches and training
sessions (Impellizzeri et al., 2004). HR methods could be
useful tools to determine the intensity range of referee’s
endurance training. In addition, given that soccer involves
numerous explosive bursts, including sprinting, turning,
and changing pace (Stølen et al., 2005), the use of the
RPE method seems to be adequate to measure internal
load during official matches, due to its recognized ability
to assess the physiological strain regardless of the type
Received: 20 March 2013 / Accepted: 21 June 2013 / Published: 01 September 2013
560
and intensity of the exercise (Impellizzeri et al., 2004;
2005). Thus, monitoring internal TL using session RPE
may allow adjusting the external TL to the physiological
strain imposed to soccer referees during official matches.
Therefore, the aim of the present study was to assess the external and internal loads of Brazilian soccer
referees during professional official matches. The knowledge of the magnitude of external and internal TL assessed in official matches may be used to develop adequate training programs for soccer referees.
Monitoring load in Brazilian referees
GPS (see Figure 1). This protocol was based on a recent
study designed to analyze the validity and reliability of
GPS receivers, performed by two moderately-trained
males in eight bouts of a standard circuit that consisted of
six laps around a 128.5 m route involving changes of
directions (Coutts and Duffield, 2010). After the validation study, all referees were trained to use the Garmin®
Forerunner 405. The GPS was switched “on” and “off”
before and after the first and second halves of each match,
respectively.
Methods
Subjects
Eleven Brazilian soccer referees (age 36.2 ± 7.5 years;
refereeing experience 8.3 ± 5.1 years; body mass index
24.8 ± 1.9 kg·m-2; body fat 14.6 ± 5.6%) that officiated
during the 2009-2010 season volunteered to participate in
this study. Subjects were informed of the experimental
risks and benefits, and signed an informed consent form
prior to the investigation. The investigation was approved
by an Institutional Review Board for use of human subjects.
Design
This observational study was designed to assess the external and internal loads of Brazilian field soccer referees
during professional official matches. Acknowledging the
specific demands of these professionals in an actual environment is crucial to provide relevant information to
develop adequate and specific training strategies (Impellizzeri et al., 2004; 2005; Moreira et al., 2012). For this
study, 11 field referees (all of them with at least three
years of refereeing experience) were examined during 35
professional soccer matches of the Rio Grande do Norte
state championship (i.e., northeast region of Brazil). It is
noteworthy that none of the teams of this championship
participates in the First Division of the National Soccer
League in Brazil. The external and internal loads were
assessed on three to four matches, for each referee. The
total distance covered, and mean and maximal running
speeds during the soccer matches were used as indices of
the external load. The session RPE and the Edwards'
methods were assumed as indices of the physiological
strain (i.e. internal load) imposed on the referees during
the matches.
Methodology
Total distance covered (km), distance covered at the highintensity HR zone (90-100% of HRmax), and mean and
maximal running speeds (km·h-1) were assessed using a
wrist GPS receiver with an HR monitor (Garmin® Forerunner 405, Olathe, USA) (Ardigò, 2010). Before the
commencement of the study, the Garmin® Forerunner 405
was validated using a 100-meter route with changes in
direction at different speeds – 5 km·h-1 (40 times) and 10
km·h-1 (40 times) – (Figure 1). Two professional athletes
(1.82 ± 0.71 m, 79.6 ± 4.4 kg, VO2max = 55.5 ± 2.1 mL·kg1
·min-1) participated in this preliminary validation study.
The actual route distance was determined using a measuring tape to compare with the distance registered by the
Figure 1. One hundred meter route with changes of directions.
The session RPE internal TL was determined by
multiplying the match duration (minutes) by the RPE
assessed 30 min after the end of the second half of each
soccer match (Foster et al., 2001). All referees were familiarized with the modified CR10-scale (Foster et al.,
2001) before the beginning of the study. The Edwards’
TL was calculated for all matches (Edwards, 1993). The
Edwards’ TL method (Edwards, 1993) estimates the internal load based on five HR zones, as follows: 50-60% of
HRmax = 1; 61-70% of HRmax = 2; 71-80% of HRmax = 3;
81-90% of HRmax = 4; 91-100% of HRmax = 5) which
scores are added. In the present study, the HRmax was
obtained via measuring the maximal HR reached in the
match (Helsen and Bultynck, 2004).
Statistical analysis
Referee data of all assessed matches were combined and
averaged for statistical analysis purposes. All data showed
normal distribution (Shapiro-Wilk test). Data are presented as means, standard deviation (SD), and coefficient
of variation (CV). In the GPS validation preliminary
study, a paired t-test was used to compare the actual distance with the distance registered by the GPS. The Bland
and Altman (1986) plot was used to calculate the limits of
agreement between the actual distance and the distance
registered by the GPS. Changes in external and internal
loads between the first and second halves of the matches
were determined using paired t-tests. Pearson’s product-
561
Costa et al.
Table 1. Results for the Garmin® Forerunner 405 validation study.
n = 80
5 km·h-1 (n = 40)
104.0
(10.1)
*
109.5 (8.4) *
Distance (m)
[9.7%]
[7.7%]
[CV]
Limits of agreement
-5.6%
Lower limit (CI 95%)
1.2%
Upper limit (CI 95%)
10 km·h-1 (n = 40)
98.5 (8.6)
[8.7%]
Mean difference
3.4%
SD = standard deviation; CV = coefficient of variation; CI 95% = 95% confidence interval; * = significant difference in relation to
the actual distance (100m). Data expressed in mean and (±SD).
moment correlations were used to examine the relationship between session RPE TL, external load parameters
(total distance covered, distance covered at 90-100% of
HRmax, and maximal speed), and Edwards’ TL. The magnitude of these correlations was qualitatively assessed,
according to Hopkins et al. (2009) as follows: trivial r <
0.1, small 0.1 < r < 0.3, moderate 0.3 < r < 0.5, large 0.5 <
r < 0.7, very large 0.7 < r < 0.9, nearly perfect r > 0.9 and
perfect r = 1. The significance level was set at 5% (p <
0.05).
= significant correlation; * = Large correlation according to Hopkins et
al. 2009; ** = Nearly perfect correlation according to Hopkins et al.
2009.
Results
Discussion
Data obtained for the Garmin® Forerunner 405 validation
study are presented in Table 1. Results showed a small,
but significant difference between the actual distance and
the distance registered by the Garmin® Forerunner 405
(~4% of the actual distance).
The external load imposed on the Brazilian referees during official matches and the differences between
the first and second halves of the matches are presented in
Table 2.
The aim of the present study was to assess the external
and internal loads in Brazilian soccer referees during
professional official matches. The main results of this
study were: a) the distance covered by Brazilian soccer
referee was ~10.5 km; b) the mean speed and maximum
speed were 6.5 and 19.3 km·h-1, respectively; c) during
~95% of the match, the Brazilian soccer referees sustained HR level ≥ 80% of HRmax; d) the time spent at
high-intensity (90-100% of HRmax) was higher in the first
half than in the second half; e) there was a positive correlation between session RPE TL and external load related
parameters; and f) there was a positive correlation between objective (Edwards’ TL) and subjective (session
RPE TL) methods of quantifying internal load.
To date, there are no comprehensive data available
regarding the physical demand imposed on soccer referees in South America official matches. Only one study,
carried out in Brazil by Da Silva et al. (2008) assessed
energy expenditure and physical activity during official
matches. The aforementioned study was performed during
the Paraná Championship (state level) and verified that
the referees covered a distance of ~9 km per match, a
lower distance than the reported herein (~10.5 km). The
findings of the present study indicate lower covered distance than in main European soccer leagues (Castagna et
al., 2004; Castagna and Abt, 2003; Weston et al., 2010;
2011a; 2011b) but similar distance to those achieved in
international top-class tournament (Bárbero-Álvarez et
al., 2012; Mallo et al., 2009). More specifically, the Brazilian soccer referees covered a shorter distance than
Italian referees (~11.5-13.0 km) (Castagna et al., 2004;
Castagna and Abt, 2003), English referees (~11.3-12.2
km) (Weston et al. 2010; 2011a; 2011b), and referees that
officiated in the UEFA Championship (~11 km)
(Castagna et al., 2004). However, the distance covered by
the referees of the present study was similar to the referees that officiated in the 2007 America’s Cup (~10.2 km)
(Barbero-Álvarez et al., 2012) and 2005 FIFA Confederations Cup (~10.2 km) (Mallo et al., 2009), two Interna-
Table 2. Physical demands on Brazilian soccer referees
during official matches: 1st vs. 2nd halves of matches.
Variables
1st half
2nd half
5 219 (205)
5 230 (237)
Distance covered (m)
6.6 (.4)
6.4 (.3) *
Mean speed (km·h-1)
19.3 (1.0)
19.4 (1.4)
Maximum speed (km·h-1)
* = significant difference between 1st and 2nd half.
The data regarding to the internal load are exposed
in Table 3. It is important to highlight that during ~95%
of the match, the Brazilian soccer referees demonstrated a
HR ≥ 80% of HRmax.
Table 3. Mean and maximum HR (bmp), and time (min)
spent in the HR zones during official matches. Data are
means (±SD).
Variables
1st half
2nd half
166 (7)
165 (8)*
Mean HR
184 (7)
184 (8)
Maximum HR
.34 (.90) (.7%)
.22 (.47) (.5%)
HR zone 60-70%
HR zone 70-80% 2.00 (2.22) (4.1%) 3.28 (3.93) (6.8%)*
HR zone 80-90% 17.0 (9.0) (35.2%) 19.6 (8.3) (40.5%)*
HR zone 90-100% 28.9 (10.4) (59.9%) 25.3 (10.5) (52.3%)*
* = significant difference between 1st and 2nd half.
Regarding to the correlation analysis between external and internal load parameters, the data are exposed
in the Table 4. Additionally, a large correlation between
the objective (Edwards’ TL) and subjective (Foster’s
session RPE TL) methods to evaluate internal load was
observed (r = 0.61; p < 0.05).
Table 4. Correlation analysis between external and internal
load parameters in Brazilian soccer referees during official
matches. (Pearson’s product-moment).
Session RPE TL
Total distance covered (m) .
.
Distance covered at
90-100% HRmax (m)
.
Maximal speed (km·h-1)
Edwards’ TL
.38
.62 a,*
.
.
.22
.94 a,**
.54 a,*
.
.31
a
562
tional top-class tournaments.
The results of the present study may be considered
valid despite the verified difference between the actual
distance and the distance registered by the Garmin® Forerunner 405 during the GPS validation. The observed difference was small (~4%) and cannot be viewed as a limitation or a threat to presented findings, but as a systematic
error of the device. Recently, Ardigò (2010) showed that
the GPS (Garmin® Forerunner 305) can be a good and
inexpensive method to assess the external load imposed
on soccer referees during official matches. Ardigò (2010)
reported that soccer referees of the sixth and seventh
divisions of the Italian Championship covered a total
distance of 11394 ± 697 m, which are similar to those
observed in other studies involving Italian soccer referees
with video match analysis (Castagna et al., 2004;
Castagna and Abt, 2003; Tessitore et al., 2007). However,
Ardigò (2010) emphasized that, in order to achieve a
definitive proof of method accuracy, the GPS method
should be concurrently validated against the established
gold standard (i.e., video match analysis).
During all matches, in the present study, the mean
HR was ~165 bpm (~89% of HRmax). This result is higher
than that reported by Ardigò (2010) (82% of HRmax),
Tessitore et al. (2007) (84% of HRmax), and Helsen et al.
(2004) (85% of HRmax). This difference can be attributed,
at least in part, to the methods used to define HRmax. As
regards the time spent at high-intensity during the match,
the referees analyzed demonstrated a decreased time spent
at 90-100% of HRmax during the second half: ~60% vs.
~52% (-8%), respectively. This pattern is similar to that
found by Ardigò (2010), where HR was > 85% of HRmax
in 38% of the match, with ~20% decrease in the second
half. Tessitore et al. (2007) also reported a HR > 85% of
HRmax during ~60% of the first half and ~45% (-15%) of
the second half. Additionally, Tessitore et al. (2007) reported a higher blood lactate concentration after the first
match half (1.5-11.7 mmol·L-1) and lower value observed
at the end of the match (1.3-5.7 mmol·L-1). In the present
study, it was also observed that the mean speed (km·h-1)
was higher in the first half when compared to the second
half (Table 2). These results indicate a significant reduction in the match intensity during the second half. Therefore, the referees′ training programs should be designed to
improve endurance capacity at high-intensity minimizing
the performance decrement during the second half of the
match.
One possible explanation for the lack of correlation
between the Edward’s TL and the external load parameters may be attributed to the non-steady-state nature of
soccer. During intermittent activities, HR responds relatively slowly to abrupt changes in work rate and it may
not accurately reflect changes in VO2 (Achten and Jeukendrup, 2003; Tumilty, 1993). Considering the intermittent nature of the high-intensity work during official soccer matches (Bangsbo, 1994a; 1994b; Reilly, 1997), the
usefulness of HR-based methods for measuring internal
load might be limited and their validity questioned (Impellizzeri et al., 2005). The present study seems to corroborate the above-mentioned aspects, as only session
RPE method was able to determine the impact of external
Monitoring load in Brazilian referees
load on the internal load of soccer referees during official
matches.
The session RPE scores of the referees varied from
5.5 to 8.0 (i.e., “hard” to “very hard”). This data was very
similar to those reported by Weston et al. (2006) with
English referees during matches of the Football League
(i.e. below the Premier League; 6.9 ± 0.8), but lower than
reported by the same referees during the matches of the
Premier League (7.8 ± 0.8). Additionally, the authors
showed a significant moderate correlation between mean
match HR and RPE score (r = 0.48) (Weston et al., 2006).
These results indicate the validity of session RPE as a
measure of global match intensity in soccer referees, and
the tendency of higher magnitude of internal load as the
level of the competition increases. In the present study, it
was detected a similar correlation between session RPE
and mean HR, but not statistically significant (r = 0.47; p
= 0.14), possibly due the small sample size and number of
matches analyzed. In a more recent study, Weston et al.
(2010) showed a TL of 646 ± 140 AU of English referees
that officiated in the Premier League, also very similar to
the presented data (650 ± 89 AU). Weston et al. (2010)
also evidenced that the “old” referees (43-48 years)
showed higher session RPE values than the “intermediate” (37-42 years) and “young” (31-36 years) referees.
Moreover, the older referees covered a lower total distance during the matches and performed a lower number
of high-intensity activities than the intermediate and
young ones.
Session RPE is a valid method for quantifying internal load, as it represents the subject’s perception regarding the stress imposed on the organism during training sessions and competitions, which may include both
physiological and psychological aspects. Thus, this
method seems to be adequate to determinate the magnitude of internal load in a competitive environment (Weston et al., 2006; 2010; Foster et al., 2001) as several external conditions may affect the psychological perception
of the environment, as shown in the present study. Moreover, the session RPE method is easy to use, quite reliable, low cost and consistent with objective physiological
indices of the intensity of physical training (or official
matches), even in intermittent sports (Alexiou and Coutts,
2008; Foster et al., 2001; Impellizzeri et al., 2004; 2005;
Kelly and Coutts, 2007).
Additionally, there was a large correlation between
session RPE TL and Edwards’ TL (r = 0.61). Similarly,
very large correlations were found by Impellizzeri et al.
(2004) in male soccer players (r = 0.71) and by Alexiou
and Coutts (2008) in female soccer athletes (r = 0.85)
during training sessions and matches. Moreover, Weston
et al. (2006) observed a significant moderate relationship
between mean match HR and match RPE score (r = 0.48).
Taken together, it is reasonable to conclude that HR and
RPE measurements can provide relevant information
about the magnitude of internal stress, and consequently,
ensuring that appropriate loads are implemented during
training sessions.
It is important to acknowledge, as previously reported by Weston et al. (2011b), that the match demands
of soccer referees are highly variable from match to
Costa et al.
match. Therefore, it is possible that, although session RPE
and HR might be practical measures of overall internal
load, these markers may not be sensitive enough to detect
these fluctuations in external load performed. This is an
important implication for referee training programs, warranting further research.
Conclusion
In summary, Brazilian soccer referees demonstrated high
external and internal loads during official matches. The
use of portable GPS/HR monitors may be an interesting
tool for monitoring parameters related to internal (e.g.
HR) and external loads (e.g. distance and speed) of soccer
referees during official matches. However, it is important
to mention that the portable GPS/HR monitors should be
compared with the current established gold standard for
definitive conclusions in relation to its validity. The HR
data support the adoption of high-intensity intermittent
training sessions by referees, which should aim for intensities above 80% of HRmax. In addition, based on presented results, the session RPE method seems to be a
valuable marker of internal load imposed on soccer referees during official matches.
Acknowledgments
The authors would like to thank the FAPESP (Fundação de Amparo à
Pesquisa do Estado de São Paulo; grant 2012/20309-3). The authors
also wish to acknowledge all referees involved in this study for their
committed participation. Also, we would like to thank the reviewers for
the relevant contributions.
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Monitoring load in Brazilian referees
during match-play in FA Premier League referees and players.
Journal of Sports Sciences 29, 527-532.
Key points
• High external and internal loads were imposed on
Brazilian soccer referees during official matches.
• There was a high positive correlation between a subjective marker of internal load (session RPE) and
parameters of external load (distance covered between 90-100% of HRmax and maximal speed).
• There was a high positive correlation between session RPE method and Edwards’ method.
• Session RPE seems to be a reliable marker of internal load.
• The portable GPS/HR monitors and the session RPE
method can provide relevant information regarding
the magnitude of external and internal loads of soccer referees during official matches.
AUTHORS BIOGRAPHY
Eduardo Caldas COSTA
Employment
Assistant Professor at the Department of
Physical Education, Federal University of
Rio Grande do Norte, Brazil.
Degree
PhD
Research interests
Psychophysiological responses to physical
exercise and training, methods for monitoring and quantifying training loads.
E-mail: [email protected]
Caio Max Augusto VIEIRA
Employment
Graduate student at the Department of Physical Education, Federal University of Rio
Grande do Norte, Brazil.
Degree
Graduate
Research interests
Physical conditioning, training and coaching.
E-mail: [email protected]
Alexandre MOREIRA
Employment
Associate Professor at the Department of
Sport, School of Physical Education and
Sport, University of São Paulo, Brazil.
Degree
PhD
Research interests
Methods for planning, monitoring, and quantifying training; stress tolerance, hormonal
and mucosal immune responses, and managing fatigue and recovery in sport athletes.
E-mail: [email protected]
Carlos UGRINOWITSCH
Employment
Associate Professor at the Department of
Sport, School of Physical Education and
Sport, University of São Paulo, Brazil.
Degree
PhD
Research interests
Neuromuscular adaptations to strength training, training periodization.
E-mail: [email protected]
Carlo CASTAGNA
Employment
Head of the Football Training and Biomechanics Laboratory of the Technical Department of the Italian Football Association
(FIGC), Coverciano (Florence), Italy.
Degree
PhD
Research interests
Soccer field-testing and training optimization
for elite and young soccer players and referees.
E-mail: [email protected]
Marcelo Saldanha AOKI
Employment
Associate Professor at the School of Arts,
Sciences and Humanities, University of São
Paulo, Brazil.
Degree
PhD
Research interests
Psycho-neuro-immune-endocrine responses
to sports training.
E-mail: [email protected]
Eduardo Caldas Costa
Department of Physical Education, Federal University of Rio
Grande do Norte, Brazil.
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